Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants may be composed of gaseous compounds such as, for example, oxides of nitrogen (NOx). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of gaseous compounds emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. In order to ensure compliance with the regulation of these compounds, the regulating agencies have required the use of sensors located at the tail pipe opening of the engine.
Although sensors for measuring the gaseous emissions of engines are currently available in today's market, the sensors can, over time, lose their sensitivity. That is, the sensors and other components affecting sensor readings may become corroded, covered with layers of dirt, exposed to temperature extremes, or suffer other performance-degrading effects. In response to this exposure, the accuracy of the readings from the sensor may drift away from an acceptable range. In order to ensure continued performance of the sensors, the sensors must be periodically recalibrated.
In the past, calibration of such a sensor was accomplished outside of the typical operating environment of the sensor. Specifically, the sensor was removed from its operating environment (i.e., the engine or the furnace into which it was installed) and sent to a lab or installed into a separate calibration machine. The accuracy of the sensor was then tested, and the sensor recalibrated for any drift that might have occurred. Although this method may have improved the readings from the sensor, it was difficult, time-consuming, and expensive. In addition, other factors external to the sensor that could be affecting the drift were not accounted for.
One method utilized to decrease the amount of time and resources consumed during sensor calibration is described in U.S. Pat. No. 4,532,013 (the '013 patent) issued to Dietz et al. on Jul. 30, 1985. Specifically, the '013 patent discloses testing and recalibrating an engine's sensor in situ. The sensor is calibrated by exposing it from time to time to ambient air, of known oxygen concentration. Since automotive vehicles, as well as many heating or furnace installations, are not operating continuously around the clock, use of ambient air is feasible and eminently suitable as a reference gas. When the combustion process is interrupted, it is thus possible to calibrate the sensor by comparing the current output of the air-exposed sensor to a reference current value. If the deviation between the current output with the reference current value from original data is excessive, a fuel/air adjustment element is disabled and an alarm is sounded. In addition, the sensor may be adjusted to bring the accuracy of the sensor back within an acceptable range.
Although the method described in the '013 patent may suitably recalibrate a sensor, it's use may be limited. Specifically, because the sensor may be calibrated only when the engine is turned off, the method may be inapplicable to machines that operate continuously. Further, even for those vehicles whose operation is periodically interrupted, the readings from the sensor may still drift undesirably during operation, depending on the time duration between these calibration opportunities.
The exhaust system of the present disclosure solves one or more of the problems set forth above.